Service manual

5-52 AlphaServer 4000/4100 Service Manual
5.4.10 Command Codes
Table 5-9 shows the codes for transactions on the system bus and how they are
affected by the commander in charge of the bus during the transaction. The
command is a six-bit field in the command address (bits<5:0>). Bit-to-text
translations give six-bit data (although the top two bits may or may not be relevant).
Note that address bit<39> defines the command as being either a system space or an
I/O command.
Table 5-9 Decoding Commands
5 4
MC_C
MD
3 2 1 0
CMD
in
Hex
MC_
ADR
<39> Description
No B-
Cache
CPU
B-
Cache
CPU IOD
x x 0 0 0 0 X 0 1 Mem Idle Y Y
0 0 0 0 1 0 0 2 1 Write Pend Ack Y
x x 0 0 1 1 X 3 1 Mem Refresh
x x 0 1 0 1 X 4 0 Set Dirty Y
x 0 0 1 1 0 0/2 6 0 Write Thru - Mem Y Y
x 0 0 1 1 0 0/2 6 1 Write Thru - I/O Y Y
x 1 0 1 1 0 3/1 6 0 Write Back - Mem Y Y
x 1 0 1 1 0 3/1 6 1 Write Intr - I/O Y
0 0 0 1 1 1 0 7 0 Write Full - Mem Y
1 0 0 1 1 1 2 7 0 Write Part - Mem
(B-cache CPU
only)
Y
x 0 0 1 1 1 0/2 7 1 Write Mask - I/O Y
x 0 0 1 1 1 0/2 7 0 Write Merge -
Mem
Y
x x 1 0 0 0 X 8 0 Read0 - Mem Y Y Y
x x 1 0 0 0 X 8 1 Read0 - I/O Y Y
x x 1 0 0 1 X 9 0 Read1 - Mem Y Y Y
x x 1 0 0 1 X 9 1 Read1 - I/O Y Y
x x 1 0 1 0 X A 0 Read Mod0 -
Mem
YY Y